$9$ is what percent of $20$ ?
Solution: Having a percent of something means that you get that percent out of every $100$ We can set up a proportion to find out what percent of $20$ we need to take to get $9$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{\text{part}}}{{\text{whole}}}$ Which things do we know, and what are we trying to find? We are trying to find the ${\text{percent}}$ . Is $20$ the ${\text{part}}$ or the ${\text{whole}}$ The $20$ is the ${\text{whole}}$ . This means the ${\text{part}}$ is $9$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{9}}{{20}}$ If we multiply the denominator of the fraction on the right by $5$ , it will be the same denominator of the fraction on the left. To keep things equal, let's also multiply the numerator on the right by $5$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{9 \times 5}}{{20 \times 5}}$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{45}}{{100}}$ $ {\text{percent}} = {45}$ So $9$ is $45\%$ of $20$.